The present invention relates to a threshing unit for combine harvesters comprising a cylinder, an assigned concave, and at least one drum downstream of the cylinder.
In the case of known single-drum and multiple-drum threshing units of combine harvesters, impellers and/or separating cylinders are always disposed downstream of the cylinder and are used to further convey the threshed crop material to the remaining-grain separating units in the form of straw walkers or rotating separating units. Such impellers and/or separating cylinders are already known in various embodiments and configurations.
For example, document DE 196 31 866 A1 describes a threshing unit for a combine harvester in which an impeller disposed downstream of the cylinder has a revolution or peripheral speed that is dependent on the cylinder. In that particular case, this dependence is adjusted in a stepped manner by way of a transmission, or steplessly by way of a variator transmission.
Furthermore, document DE 10 2007 006 926 A1 makes known a drive device for a cylinder and an impeller, in which the cylinder is driven primarily and, by way thereof, the impeller is driven directly by a V-belt drive, wherein the impeller rotates at a speed or peripheral speed that is the same as or slightly higher than that of the cylinder.
In the case of both known drive variants, however, positioning the cylinder and the impeller relative to one another in a certain manner is neither provided nor even possible, due to the structural design of the drive. Consequently, if a conveyor slat disposed on the periphery of the impeller is situated opposite the intermediate space between two adjacent threshing slats of the cylinder, the impeller slat presses crop material into the intermediate space between the threshing slats, with the result that the crop material is not scraped off adequately and begins to circulate above the cylinder. Likewise, if a threshing slat is located opposite the intermediate space between two adjacent conveying slats of the impeller, the threshing slat of the cylinder presses crop material into the intermediate space between two adjacent conveying slats of the impeller slats. Due to the very large gap between a threshing slat and the impeller, all of the crop material is not transferred, and some crop material therefore begins to circulate above the cylinder.
In both of the aforementioned positions, the result is an impairment of the threshing and conveying process, and a resulting reduction in the output of the combine harvester.